Answer:
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Step-by-step explanation:

A regular n-gon has n lines of symmetry
The angle of rotational symmetry for regular n-gon is 360 / n degrees.
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Answer:
a₄=8n+1= -39.
Step-by-step explanation:
1) if a₁=3n; a₃=5n-6 and a₅=11n+8, then it is possible to calculate the difference according to 0.5(a₅-a₃)=0.5(a₃-a₁). Then
2) 0.5(11n+8-5n+6)=0.5(5n-6-3n); ⇔ 6n+14=2n-6; ⇔ n= -5.
3) if n=-5, then the 4th term is:

or a₄=-39.